how to handle NA values in aggregate()

Dear All:

I am trying to calculate four columns' means in a dataframe like this:

FID  MID     IID         EW_INCU EW_17.5   EMW        EEratio
1   4621  TWF2H5    45.26        NA             15.61         NA
1   4621  TWF2H6    48.02        44.09         13.41      0.3041506
2   4630  TWF2H19   51.44       47.81         NA             NA
2   4631  TWF2H21   NA          52.72         16.70      0.3167678
2   4632  TWF2H22   55.70       50.45         16.48      0.3266601
2   4633  TWF2H23   44.42       40.89         12.96      0.3169479

I try this code

aggregate(df[,4:7],df[,1],mean)

But I couldn't set the agrument na.rm=T in the mean() function,so the
results are all NAs

Please tell me how to handle NA values in the use of aggregate()

Thanks a lot

Yao He
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Master candidate in 2rd year
Department of Animal genetics & breeding
Room 436,College of Animial Science&Technology,
China Agriculture University,Beijing,100193
E-mail: yao.h.1988 at gmail.com
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